The present invention relates to a process for the catalytic transformation of one or more organic compounds that, together with unwanted attendant materials, form a starting substance.
In chemistry the necessity frequently exists to carry out a catalytic transformation or conversion of a mixture of organic compounds that, along with the desired starting substance, contains undesired attendant or impurity substances, which either interfere with the catalytic reaction or are unwanted and undesired in the final product. Among the catalytic reactions that are under consideration in this context are included, for example, alkylation, acylation, esterification, transesterification, oxidation, or hydrogenation reaction, all of which are well known and understood in the art. The starting substances to carry out these reactions can be natural or synthetic.
A commercially very important example of such a reaction is the catalytic hydrogenation of fats, oils, fatty acid esters and free fatty acids from natural sources, which are also referred to herein as fatty raw materials. The objective of the hydrogenation of these organic compounds is to hydrogenate partially or completely the double bonds, without affecting other functional groups of the compounds, for example the carboxyl group, in the process. The complete hydrogenation of these compounds is characterized as hardening, since their melting points are increased by this. If it is intended that only a certain number of the double bonds be hydrogenated, then it is referred to as selective hydrogenation. The hydrogenation occurs catalytically with the assistance of hydrogen.
Fats and oils from natural sources contain attendant and impurity substances, which are undesired in their later application and also act as catalysts poisons and lead to a faster deactivation of the hydrogenation catalysts. Within the context of this invention, all substances that decrease the catalytic activity--regardless of their chemical nature or their source--are characterized as catalyst poisons. It therefore involves the naturally occurring materials in fats and oils, as well as decomposition products or materials that are, however, introduced during the processing and reactions (H. Klimmek, JAOCS, Vol. 61, No. 2, Feb. 1984). This category of undesired components includes in particular sulfur, phosphorous, chlorine and nitrogen compounds, as well as, for instance oxidized fatty acids, soaps and water.
Before the hydrogenation takes place of the fats, oils, fatty acid ester and free fatty acids, the starting substances are therefore liberated from the undesired attendant materials in a separate step. This can take place with fats and oils through a chemical or physical refinement process and with free fatty acids that usually are refined through vacuum distillation. According to the degree of purity of the starting materials, the purification process can be carried out in stages. In vacuum distillation for the purification of free fatty acids, decomposition products can indeed result, since the fatty raw materials are easily thermally decomposable. The decomposition products frequently cause an unpleasant odor of the distilled products, which must be remedied by deodorization. The deodorization is carried out only after the hydrogenation. Because of the thermal sensitivity of the products, with a short contact time, a low temperature in the processing is to be maintained as much as possible.
Since about 1970, condensed gases have been used for the extraction, refinement, deodorization and fractionation of fatty raw materials, as for example in DE 23 63 418 C3, U.S. Pat. No. 4,156,688, DE 35 42 932 A1, DE 42 33 911, DE 43 26 399 C2, EP 0 721 980 A2 and DE 44 47 116 A1. These processes describe the use of condensed gases in the subcritical (liquefied), near critical and supercritical condition, whereby compared to the distillation procedures, the processes using condensed gases are conducted under relatively favorable processing conditions.
Today, cooking oils and free fatty acids are hardened to the extent of over 99%, either batch wise in a stirred tank, or in tubular reactors. In these process, powder form nickel-diatomite or nickel-silica catalysts are used for hydrogenation, which catalysts must be removed through filtration after the hydrogenation. Disadvantageously, in such processes, there are low space-time yields and the formation of undesirable side products as a consequence of the limited transport of hydrogen to the catalyst by diffusion from the gas phase through the liquid phase. Moreover, these processes have high costs, for example, for personnel, energy and filtration. The filtration decreases the product yield, since hardened product remains in the filter residue.
The nickel-diatomite or nickel-silica catalyst forms a considerable portion of so-called trans-fatty acids in the hardening of cooking oil. This fact is of particular disadvantage, since trans-fatty acids are suspected of increasing the fatty content and cholesterol content in human blood.
With the hardening of free fatty acids for oleo-chemical applications, the nickel-diatomite or nickel-silica catalyst deactivates through the formation of so-called nickel soaps. These remain in the product and must be separated by distillation. Nickel soaps represent a waste product and must be removed at considerable cost.
For the avoidance of the previously mentioned disadvantages of the batch hardening, or the use of nickel-diatomite or nickel-silica catalysts, continuous processes were developed in which palladium fixed bed catalysts come into use. The patents, or patent applications that describe the state of the art on this are CA 1 157 844, DE 41 09 502 C2 and DE 42 09 832 A1 or EP 0 632 747 B1.
According to DE 41 09 502 C2, the continuous hardening of crude fatty acids in the trickle bed is carried out with a palladium/titanium oxide catalyst. The reaction media are therefore added in the form of a 2-phase mixture of liquid fatty acids and hydrogen gas with the fixed bed catalyst for the reaction. The hydrogenation activity in this process thereby permits a space velocity of only 1.2 h.sup.-1. The catalyst in this process has a limited resistance to the catalyst poisons contained in the crude fatty materials. Also here, a separate purification of the starting substances cannot, however, be foregone in the industrial application of the catalyst for the reduction of the catalyst consumption.
WO 95/22591 and WO 96/01304 describe processes in which super-critical fluids are used as solvents for fats, oils, free fatty acids, free fatty acid esters and hydrogen. According to WO 95/22591, the cited compounds with the hydrogen necessary for the hydrogenation and in the presence of a supercritical fluid are thereby transformed with a catalyst, and then separated by it through release of the supercritical fluid. The supercritical fluids make possible in this process an improved material transport, in particular for hydrogen, and an improved heat exchange. Moreover, the viscosities of the reaction medium are lowered, so that clearly increased space time yields and improved selectivity can be obtained. No statements are made for the necessary purity of the starting substance for this process.
Through the purification stages added as a rule to the hydrogenation process, one manages to clearly lower the consumption of catalyst per ton of hardened fatty acids in the batch hardening with nickel-diatomite or nickel-silica catalyst, as well as in the continual hardening in the presence of supercritical fluids.
U.S. Pat. No. 3,969,382 describes the simultaneous hydrogenation and deodorizing of fats and oils in the presence of supercritical carbon dioxide, hydrogen and a finely divided nickel-hydrogenating catalyst at temperatures of 100 to 250.degree. C. and a pressure of 150 to 300 bar. The catalyst, after the hydrogenation, is separated out from the hardened products through a filter press. The simultaneous hydrogenation and deodorization has the disadvantage, that the catalyst comes directly into contact with the catalyst poisons and is deactivated.
The state of the art for the hydrogenation of fatty raw materials thus describes batch or continuous processes, which, nevertheless, are only in a limited way insensitive to the catalyst poisons contained in the starting substance, and which, as a rule, require the purification of the starting substance in a separate stage of purification. Similar relationships occur with the other processes carried out as pure treatments.
An object of the present invention is therefore to provide a process for the catalytic transformation or conversion of organic compounds, which makes possible the purification of the starting substance and the catalytic transformation of the organic compounds in a single process.